2.1 Osseous Tissue Histology & Physiology &2.2 Skeletal System Overview Flashcards
skeletal system
consists of the bones, its associated cartilages, & the joints. Its two divisions are the axial & the appendicular skeleton.
axial skeleton
composed of the bones of the head, neck, & trunk—specifically, the cranial, facial, vertebral column, hyoid, auditory ossicles, sternum, & rib bones.
appendicular skeleton
consists of the bones of the upper limbs, the lower limbs, the pectoral girdle (the bones forming the shoulder joint), & the pelvic girdle (the bones forming the pelvis & hip joint).
Shapes of Bones
common bone shape include: long, flat, short, & irregular.
Compact vs Spongy Bone
- Compact bone is the hard, solid outer layer of the bone. It’s dense and strong, helping protect and support the bone.
- Spongy bone is the inner layer, which is lighter and looks like a sponge with tiny holes. It’s not as solid, but it helps reduce the bone’s weight and has spaces where bone marrow (which makes blood cells) can be found.
- So, compact bone is on the outside and spongy bone is on the inside, making bones strong but not too heavy.
The Osteon
- the basic unit of bone tissue, kind of like the building block of bone.
- In compact bone, osteons are packed tightly together and look like tiny cylinders.
- In spongy bone, osteons are scattered and are part of a network of flat plates (called trabeculae) and spiny rods (called spicules).
Lamellae
- Each osteon is made of several layers of bone tissue called concentric lamellae (singular: lamellae)
- These layers are circular and spiral around a central space, called the central canal, which contains blood vessels and nerves.
There are three types of lamellae:
Concentric lamellae: The layers that form the circular structure of the osteon around the central canal.
Interstitial lamellae: These are found between osteons, filling in the gaps.
Circumferential lamellae: These are the outermost layers, running around the edge of the bone, just beneath the surface.
This structure helps bones stay strong and flexible, while also allowing for blood and nerve supply.
Osteocytes
- In between each lamellae sit the osteocytes (mature bone cells), which live in small gaps/pits/holes in the bone matrix called lacunae (singular: lacuna)
- osteocytes are able to communicate with each other and the rest of the body through tiny channels called canaliculi, which go through the hard bone matrix.
lacunae (or lacuna)
- lacunae are found between the layers of bone tissue, or lamellae
- small gaps/pits/holes in the bone matrix
- Each lacuna has an osteocyte inside it.
osteoblasts
- cells that build new bone.
- producing the bone matrix, which is made up of collagen fibers and other substances that give bone its strength.
- basically, produce collagen fibers during bone formation
osteoclast
- cells that break down or “dissolve” bone tissue.
- help with the process of bone remodeling by removing old or damaged bone, making space for new bone to be built.
- important for maintaining healthy bones, as it allows for the renewal and reshaping of bone over time.
Long Bones
- the bones in your limbs that are longer than they are wide, like your arms and legs.
- The long middle part of the bone is called the diaphysis.
- The ends of the long bones are called the epiphyses (plural for epiphysis)
diaphysis
- long middle part of the bone
- Inside the diaphysis is the medullary cavity, which contains yellow bone marrow (a type of fatty tissue in adults). If needed, yellow marrow can change into red bone marrow, which produces blood cells.
- During development, the diaphysis (the shaft of the bone) and the epiphyses (the ends of the bone) start off as separate pieces. As you grow, these parts eventually fuse together.
medullary cavity
- located in the diaphysis (the central shaft) of long bones.
- It’s the hollow space inside the bone, and in adults, it mainly contains yellow bone marrow
- The medullary cavity helps reduce the weight of the bone while still providing strength and structure.
- is lined by a thin layer of tissue called the endosteum.
epiphyses
- made of spongy bone, which contains red bone marrow, the tissue that makes blood cells.
- The rounded ends of the long bones
- The outer surface of the epiphysis is covered by a layer of articular cartilage, which helps reduce friction and absorb shock at the joints where the bone meets other bones.
the ends of long bones, and they play a key role in joint movement and blood cell production.
endosteum
- thin layer of tissue that lines the inside of bones
- covers the medullary cavity (the hollow space inside the bone), the spongy bone, and the canals that run through the bone.
- important because it contains cells that help with bone growth, repair, and remodeling.
like the “inner lining” of the bone, helping to maintain and repair the bone from the inside.
epiphyseal plate
- The area where the diaphysis and epiphysis meet is called the epiphyseal plate
- made of cartilage during childhood and allows the bone to grow in length. Once growth is complete, the cartilage turns into bone, and the epiphyseal plate becomes an epiphyseal line
- epiphyseal line is a visible “scar” in adults, showing where the growth plate once was. It marks the point where the bone stopped growing in length once a person reached adulthood.
periosteum (plural: periostea)
- a thin, tough layer of connective tissue that covers the outer surface of bones (except where there’s cartilage).
- It helps protect the bone and plays a role in bone growth and repair.
- connected to the bone by perforating fibers, which help anchor it to the bone’s surface.
deep to the periosteum is a layer of compact bone, with a layer of spongy bone under it
articular cartilage
- On the ends of the bones (the epiphyses), where they meet at joints, there’s a layer of hyaline cartilage called articular cartilage
- helps cushion the long bones wherever they meet at the synovial joints & lets the bones move smoothly at the joint with the help of synovial fluid
Compact bone
- the dense, hard outer layer of bone
- has blood vessels and nerves that enter the bone through small openings called nutrient foramina.
layers of a long bone from superficial & intermediate
- Superficial layer around the whole bone: The outer surface of the bone is covered by periosteum (except at the joints).
- Superficial layer on the epiphyses (ends of the bone): Covered with articular cartilage (to help with smooth joint movement).
- Intermediate layer: Inside the bone, you have a layer of compact bone (dense and strong).
layers of a long bone from deep
- Deep layer in the epiphyses (ends of the bone): The inside of the epiphyses contains spongy bone, which looks like a sponge with tiny holes. This spongy bone is made of trabeculae (the thin plates) and spicules (the rods or spikes).
The spongy bone is lined with endosteum, a thin layer of connective tissue that helps with bone growth and repair. - Deep layer in the diaphysis (shaft of the bone): The medullary cavity (the hollow space inside the diaphysis) is found here and contains yellow bone marrow. This cavity is also lined with endosteum, and the endosteum extends to the central canals (which hold blood vessels and nerves) and the nutrient foramina (small openings where blood vessels and nerves enter the bone).
the deep parts of the bone—both in the epiphyses and diaphysis—are lined with endosteum, helping with bone maintenance and providing support for the bone’s internal structures.
Flat Bones
- primarily found in the skull, sternum, scapula, hips, & rib bones lack a medullary cavity
- structured like a “sandwich” with two layers of compact bone surrounding a central layer of spongy bone, all lined by periosteum and endosteum.
- This deep layer of spongy bone in a flat bone is referred to as diploë (dip-lo-ee).
layers of a flat bone from superficial to deep
- Outer superficial layer lined with periosteum
- Intermediate layer of compact bone
- Deep spongy bone (trabeculae) lined with endosteum
- Intermediate layer of compact bone
- Inner superficial layer lined with periosteum
Bone Maintenance & Remodeling
- Bone tissue is very adaptable & dynamic, & constantly remodels itself to handle the stresses from daily activities.
Wolff’s Law says:
* Bones get stronger to better withstand the regular forces it encounters
* The shape of the bone os determined based on the stress it experiences.
Calcium Homeostasis
Most of the body’s calcium may be found in osseous tissue
3 hormones control calcium levels:
- Parathyroid Hormone (PTH) & Calcitriol: Both increase bone breakdown to release calcium into the blood.
PTH is released by the parathyroid glands (tiny glands near the thyroid).
Calcitriol is made by the kidneys. - Calcitonin: promotes bone deposition (mineralization) of the mineral components of bone, lowering blood calcium levels. It is released by the parafollicular cells in the thyroid gland.
If blood calcium is high, calcitonin lowers it by building bone.
If blood calcium is low, PTH or calcitriol raise it by breaking down bone and releasing calcium into the blood.
